Many electrical or electro-optical systems being developed today are modular. This gives an end customer the ability to have a low cost start up solution, to scale up if conditions demand and to upgrade/replace/mix the modules as required. The flexibility of the modular system is achieved by using modules, which plug into a rack system. Each rack has multiple apertures (or ports), which can be filled individually as necessary. When a rack is full, another may be acquired to allow for further expansion.
One problem with such a modular rack system is that some of the ports may be unused and left open. Without a port plug, this leaves an aperture through which Radio Frequency emissions can escape. These emissions can cause the system to fail the Electromagnetic Compatibility (EMC) directive, which is a standard that puts limits on the amount of emissions that can be allowed to escape.
With some racks, such as, for example, Small Form Factor Pluggable (SFP) devices, the module cage can project beyond the front face of the rack so that the rack cannot be provided with a flap or plate to cover the aperture of the unused cage. Such an open aperture also allows entry of dust into the rack, which can affect other modules within the rack as forced air cooling is often used for the whole rack. A secondary effect of an open aperture that can occur is disturbance of the airflow within the rack which may cause unforeseen hotspots since the thermal operation of the rack is generally designed to work optimally when the rack is fully loaded. This may be insignificant for the SFP platform where each module socket is surrounded by a cage, but on other pluggable devices it may have greater importance.
It is known to provide dust covers, which are often rubber or plastics mouldings, and may be metallised if they are intended to prevent EMI, but such covers are usually provided on an ad hoc basis are rarely match the remainder of the modules in the rack. Furthermore, they do not always meet requirements that may be set for the mechanical compression forces that the cover must be able to handle.